This invention relates to a valve arrangement for an internal combustion engine and more particularly to an five valve per cylinder single overhead camshaft internal combustion engine.
The advantages of using multiple valves for each cylinder of an engine are well known. One arrangement which appear to provide optimum results is a so-called "five valve" engine wherein each cylinder of the engine is served by five poppet valves. Normally such arrangements employ three intake valves and two exhaust valves. Although the use of multiple valves increases engine performance, there are a number of problems in connection with the location and actuation of multiple valves, particularly those having five or more in number.
Conventionally the valves for a cylinder head are disposed at angular relationships to a vertically extending plane passing through the center of the combustion chamber with the intake valves being located on one side and the exhaust valves located on another side. Although it has been proposed to employ a separate intake camshaft and an exhaust camshaft for operating the intake and exhaust valves, there are a number of reasons why single overhead camshaft engines may be preferred. For example, single overhead camshaft engines have a less complex cam arrangement and also the problem of synchronizing two camshafts with the crankshaft and maintaining appropriate tension and short chain lengths are simplified with single overhead cam engines.
In one proposed arrangement, the single overhead camshaft passes through the center plane of the cylinder or substantially in line with it and the valves are operated by short rocker arms. However, this type of actuating mechanism places all of the valve operating system directly between the valves and thus makes central spark plug placement difficult. If the spark plug has its gap at a central location, this normally must be accomplished by mounting the spark plug at a considerable angle to the cylinder bore axis and this is not always desirable.
In addition to the aforenoted defect, it is also desirable to maintain the valve axis at a very small angle to the cylinder bore axis so as to maintain a relatively shallow combustion chamber. This is particularly important when multiple valves are employed so as to reduce the surface area of the combustion chamber and permit high compression ratios. However, if the angle of the intake and exhaust valves is made narrow, the space between them becomes quite small and it is difficult to provide a single overhead camshaft in this area with the necessary rocker arm arrangement for operating all of the valves.
It is, therefore, a principal object of this invention to provide an improved cylinder head layout arrangement for a multiple valve engine.
It is a further object of this invention to provide an improved, single overhead cam, five valve per cylinder, cylinder head and valve arrangement.
It is a further object of this invention to provide an improved cylinder head arrangement embodying a single overhead camshaft, five valves per cylinder, and affording a central spark plug location with the spark plug extending generally parallel to the cylinder bore axis.
Another problem associated with single overhead camshaft multiple valve engines is that the length of the engine in the direction of the axis of rotation of the camshaft tends to become long and can increase the spacing between adjacent cylinder bores and provide an unduly long engine. This problem is partially caused by the number of cam lobes that must be employed for operating the multiple valves and also the placement of the bearing arrangement for rotatably journaling the camshaft.
It is, therefore, another object of this invention to provide an improved cylinder head arrangement for a single overhead camshaft engine wherein the single overhead camshaft has multiple cam lobes for operating multiple valves.
It is a further object of this invention to provide an improved bearing arrangement for rotatably journaling a camshaft having a plurality of cam lobes associated with each cylinder of the engine.
In conjunction with the use of single overhead cam engines, an arrangement has been proposed wherein some of the valves are directly operated by the camshaft while other valves are operated by rocker arms. Such an arrangement necessitates separate cam lobes for each rocker arm and each directly operated valve. However, when some of the valves are directly operated, the adjacent cam lobes must be positioned so as to avoid interference with the directly operated valve. This can also increase the length of the engine.
It is, therefore, a still further object of this invention to provide an improved valve arrangement for a multiple valve engine wherein certain valves are directly operated by the camshaft and others are operated through rocker arms while maintaining a short overall length for the valve actuating mechanism.